Engines may be configured with boosting devices, such as turbochargers or superchargers, to increase mass airflow into a combustion chamber. Turbochargers and superchargers compress intake air entering the engine using an intake compressor. While a turbocharger includes a compressor that is driven by a turbine, a supercharger includes a compressor that is driven by the engine, or by a motor. In some engine systems, one or more intake charging devices may be staged in series or parallel to improve engine boost response.
One example of a multi-staged boosted engine is shown by Kawamura et al. in U.S. Pat. No. 6,938,420. Therein, an electric supercharger driven by an electric motor and an electric supercharger bypass valve (ESBV) are staged downstream of a turbocharger. During conditions when the turbocharger compressor is not spun up, the ESBV may be closed and the electric supercharger may be rotated to provide a transient positive boost pressure in order to reduce turbo lag. Then, when the turbocharger compressor is sufficiently spun up, the ESBV may be opened and the electric supercharger may be disabled, allowing the turbocharger to provide the desired boost pressure.
In addition to intake charging devices, vehicles may be configured with on-board air and/or vacuum pumps. For example, on-board air pumps may be used for multiple purposes such as for inflating tires, inflating air suspension, etc. Likewise, on-board vacuum pumps may be used as a source of vacuum for various engine vacuum actuators, such as for fuel vapor canister purging, or a brake booster. While the additional pumps may enable a reliable source of air or vacuum to be provided, their use may be limited by their costs and sizes. In still other approaches, such as shown by Infantini in US 20160059643, a portion of compressed air delivered to the engine cylinders of an off-road vehicle (such as a plow) may be used for tire inflation. The portion of compressed air diverted may be based on the tire pressure. However, the diversion of compressed air from the engine causes the engine output to be reduced, affecting vehicle performance.
The inventors herein have recognized that an electric supercharger of a staged engine system can be combined with a pressurized air pick-up to advantageously provide the functionality of an on-board air pump and/or vacuum pump. In one example, a method for an engine comprises: during engine idling and while a vehicle is not propelled, sealing a portion of an intake passage by closing each of an intake throttle and a bypass valve coupled to an electric supercharger; operating the supercharger to generate compressed air in the sealed portion; and drawing the compressed air from the sealed portion into a device. In this way, a reliable source of compressed air and/or vacuum can be provided on-board a vehicle using existing components and without affecting vehicle performance.
As an example, an electric supercharger (ES) including a compressor driven by an electric motor may be staged upstream of a turbocharger (TC) including a compressor driven by an exhaust turbine. An electric supercharger bypass valve (ESBV) may be coupled in a bypass around the ES. During conditions when boost pressure is demanded, turbo lag may be reduced by closing the ESBV and operating the ES compressor to meet the boost demand while the turbine spools up. Once the turbine has spooled up, the ESBV may be opened and the ES compressor may be disabled while the TC compressor is used to meet the boost demand. During conditions when the engine is idling and the vehicle is stopped, the ES compressor may be opportunistically operated as an air pump or a vacuum pump and compressed air or vacuum may be stored for later use, or used in situ such as for inflating vehicle tires or operating a vacuum actuator. Therein, the ESBV may be fully closed, and the opening of the intake throttle may be reduced such that there is just enough air to allow the engine to idle (and not stall). As a result of the valve adjustments, a volume of the intake passage between the two valves may be effectively sealed off. The ES compressor motor may then be operated at full duty cycle to generate compressed air in the sealed volume. A pick-up valve coupling a pressurized air pick-up to the sealed volume may be opened to enable the compressed air to be stored or immediately used. When vacuum is desired, the compressed air may be directed through an ejector coupled to the pressured air pick-up, thereby generating vacuum at the ejector. The generated vacuum may be stored or immediately used. When driver torque demand increases, or if vehicle propulsion is requested, the pick-up valve, the intake throttle, and the ESBV may be opened, and the ES compressor may return to being operated, as required, for meeting transient boost demands.
In this way, an existing intake charging device may be advantageously used as an on-board air pump and/or vacuum pump. By reducing the need for a dedicated on-board air pump and vacuum pump, a reliable air and vacuum source is provided on-board a vehicle with cost reduction and component reduction benefits. The technical effect of sealing off a portion of an intake passage and operating an electric supercharger compressor is that compressed air may be generated and delivered into the sealed area, wherefrom the compressed air may be easily picked-up. By closing an intake throttle when operating the electric supercharger as an air or vacuum pump, engine output is not affected during the pump operation. By coupling an ejector to the pressurized air pick-up, the same compressed air generated by the supercharger may be used as an air source or a vacuum source, as needed. By operating the supercharger as an air or vacuum pump during engine idling conditions, air and/or vacuum may be opportunistically generated without affecting engine or vehicle performance.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.